LACP (Link Aggregation Control Protocol) and PAgP (Port Aggregation Protocol) are two protocols used to combine multiple physical ports into one logical port, referred to as link aggregation or channel port. The purpose of link aggregation is to increase bandwidth, redundancy, and network availability. Link aggregation is also known as EtherChannel, trunking, bundling, or bonding.
LACP and PAgP have some similarities and differences. This article will discuss what LACP and PAgP are, what are the differences and relationships between the two, and when to use one of them.
What is LACP?
LACP is a standard protocol defined by IEEE 802.3ad. LACP allows switches or other network devices to automatically configure and manage link aggregation. LACP sends LACPDU (Link Aggregation Control Protocol Data Unit) frames between ports involved in link aggregation to negotiate and synchronize port status and parameters. LACP can also detect link failures and adjust link aggregation configuration dynamically.
LACP has two modes of operation: active and passive. Active mode means the port will always send LACPDU frames to start link aggregation negotiations. Passive mode means the port will only respond to LACPDU frames received from other ports, but will not send its own LACPDU frames. To establish link aggregation with LACP, at least one port must be in active mode.
What is PAgP?
PAgP is a proprietary protocol developed by Cisco. PAgP is like LACP but only works on Cisco devices that support it. PAgP also sends PAgPDU (Port Aggregation Protocol Data Unit) frames between ports involved in link aggregation to negotiate and synchronize the port states and parameters. PAgP can also detect link failures and adjust link aggregation configuration dynamically.
PAgP has two modes of operation: desirable and auto. Desirable mode means the port will always send PAgPDU frames to start link aggregation negotiations. Auto mode means the port will only respond to PAgPDU frames received from other ports, but will not send PAgPDU frames itself. To establish link aggregation with PAgP, at least one port must be in desirable mode.
What is the Difference between LACP and PAgP?
LACP and PAgP have several differences, including:
- LACP is a standard protocol that can work on network devices from different vendors, while PAgP is a proprietary protocol that can only work on Cisco devices that support it.
- LACP uses LACPDU frames, while PAgP uses PAgPDU frames. LACPDU and PAgPDU frames have different formats and are not compatible with each other.
- LACP has active and passive modes, while PAgP has desirable and auto modes. Active and desirable modes work the same, sending frames to start link aggregation negotiations. Passive and auto modes also work the same, they only respond to received frames. However, the name of the mode differs between LACP and PAgP.
- LACP can support up to 16 ports in a single link aggregation, but only 8 ports can be active simultaneously. PAgP can support up to 8 ports in a single aggregation link, and all ports can be active simultaneously.
Here is a table comparing LACP and PAgP:
| LACP | PAgP |
| IEEE 802.3ad standard protocol | Cisco proprietary protocols |
| Work on network devices from different vendors | Only works on Cisco devices that support it |
| Using LACPDU frames | Using PAgPDU frames |
| Has active and passive modes | Has desirable and auto modes |
| Supports up to 16 ports, but only 8 ports are active | Supports up to 8 ports, and all ports are active |